Disk drives are information storage devices that use magnetic media to store data. Referring to FIG. 1a, a typical disk drive in related art has a magnetic disk and a drive arm to drive a head gimbal assembly 277 (HGA). The HGA 277 has a suspension (213) with a slider 203 mounted thereon. The disk is mounted on a spindle motor which causes the disk to spin. The drive arm is provided with a voice-coil motor (VCM) for controlling the slider 203 to move from track to track across the surface of the disk to read data from or write data to the disk.
However, because of its large inertia the VCM has limited bandwidth. Thus the slider 203 can not attain a quick and fine position control which will affect the ability of the slider 203 to read data from and write data to the magnetic disk.
To solve the above-mentioned problem, piezoelectric (PZT) micro-actuators are now utilized to modify the displacement of the slider 203. That is, the PZT micro-actuator corrects the displacement of the slider 203 on a much smaller scale, and with higher frequency components than the VCM. It enables a smaller recording track width, hence increasing the ‘tracks per inch’ (TPI) value by 50%. It also reduces the head seeking and settling time. Both the disk surface recording density and drive performance are improved.
Referring to FIG. 1b, a traditional PZT micro-actuator 205 comprises a ceramic U-shaped frame 297 which comprises two ceramic beams 207 each of which having a PZT piece (not labeled) for actuation. With reference to FIGS. 1a and 1b, the PZT micro-actuator 205 is physically coupled to a suspension 213, and there are multiple (e.g., three) electrical connection balls 209 (gold ball bonding or solder ball bonding, GBB or SBB) to couple the micro-actuator 205 to the suspension traces 210 in each one side of the ceramic beam 207. In addition, there are multiple (e.g., four) metal balls 208 (GBB or SBB) to couple the slider 203 to the suspension traces 210 for electrical connection of the read/write transducers. FIG. 1c shows a detailed process of inserting the slider 203 into the micro-actuator 205. The slider 203 is bonded with the two ceramic beams 207 at two points 206 at the opening of the U-shaped frame by epoxy dots 212. The slider 203 and the frame 297 mutually form a rectangular hollow structure. The bottom of the U-shape frame 297 is attached to a suspension tongue (not shown in FIG. 1c) on the suspension. The slider 203 and the beams 207 are not directly connected to the suspension and thus move freely with respect to the suspension.
When an actuating power is applied through the suspension traces 210, the PZT pieces on the ceramic beams 207 will expand or contract, causing the two ceramic beams 207 to bend in a common lateral direction. The bending causes a shear deformation of the frame 297. Its rectangular shape becomes approximately a parallelogram. The slider 203 undergoes a lateral translation, because it is attached to the moving side of the parallelogram. Thus a fine head position adjustment can be attained.
However, translation of the slider 203 generates a lateral intertia force which causes a suspension vibration resonance which has the same resonance effect as shaking the suspension base plate. This will affect the dynamic performance of the HGA and limit the servo bandwidth and the capacity improvement of HDD. As shown in FIG. 2b, numeral 201 represents a resonance curve when shaking the suspension base plate and numeral 202 represents a resonance curve when exciting the micro-actuator 205 shown in FIGS. 1c and 2a. Under a frequency of 20K, there are several large peaks and valleys in the suspension frequency response, which indicate a bad characteristic of resonance. The figure clearly shows the above-mentioned problem.
Referring to FIG. 2a, the U shape micro-actuator 205 is partially mounted on the suspension tongue. When the micro-actuator 205 is operated, the two side arms 207a, 207b will bend outwardly. When one side arm 207a bends along the direction 200a, it will generate a reaction force Fa in the bottom arm which is mounted on the suspension tongue. This reaction force Fa will transfer to the suspension and generate a vibration which have the same effect as shaking the suspension base plate. Similarly, when the other side arm 207b bends along the direction 200b, it will generate a reaction force Fb in the bottom arm and this reaction force Fb will also transfer to the suspension and generate a vibration which have the same effect as shaking the suspension base plate.
Hence, it is desired to provide a micro-actuator, head gimbal assembly, disk drive to solve the above-mentioned problems.